Generally, fine pattern formation is carried out by photolithography in the manufacture of a semiconductor device. A number of substrates called photomasks are normally used for such fine pattern formation. The photomask comprises generally a light-transmissive glass substrate having thereon a fine pattern made of a metal thin film or the like. The photolithography is used also in the manufacture of the photomask.
In the manufacture of a photomask by photolithography, use is made of a photomask blank having a thin film (e.g. a light-shielding film) for forming a transfer pattern (mask pattern) on a light-transmissive substrate such as a glass substrate. The manufacture of the photomask using the photomask blank comprises an exposure process of writing a required pattern on a resist film formed on the photomask blank, a developing process of developing the resist film to form a resist pattern in accordance with the written pattern, an etching process of etching the thin film along the resist pattern, and a process of stripping and removing the remaining resist pattern. In the developing process, a developer is supplied after writing the required pattern on the resist film formed on the photomask blank to dissolve a portion of the resist film soluble in the developer, thereby forming the resist pattern. In the etching process, using the resist pattern as a mask, an exposed portion of the thin film, where the resist pattern is not formed, is dissolved by dry etching or wet etching, thereby forming a required mask pattern on the light-transmissive substrate. In this manner, the photomask is produced.
For miniaturization of a pattern of a semiconductor device, it is necessary to shorten the wavelength of exposure light for use in photolithography in addition to miniaturization of the mask pattern of the photomask. In recent years, the wavelength of exposure light for use in the manufacture of a semiconductor device has been shortened from KrF excimer laser light (wavelength: 248 nm) to ArF excimer laser light (wavelength: 193 nm).
As a type of photomask, a halftone phase shift mask is known apart from a conventional binary mask having a light-shielding film pattern made of a chromium-based material on a light-transmissive substrate. This halftone phase shift mask is configured to have a light-semitransmissive film on a light-transmissive substrate. This light-semitransmissive film is made of, for example, a material containing a molybdenum silicide compound and is adapted to transmit light having an intensity that does not substantially contribute to exposure (e.g. 1% to 20% with respect to an exposure wavelength) and to produce a predetermined phase difference. By the use of light-semitransmissive portions formed by patterning the light-semitransmissive film and light-transmissive portions formed with no light-semitransmissive film and adapted to transmit light having an intensity that substantially contributes to exposure, the halftone phase shift mask causes the phase of the light transmitted through the light-semitransmissive portions to be substantially inverted with respect to that of the light transmitted through the light-transmissive portions so that the lights having passed near the boundaries between the light-semitransmissive portions and the light-transmissive portions and bent into the others' regions due to diffraction cancel each other out. This makes the light intensity at the boundaries approximately zero to thereby improve the contrast, i.e. the resolution, at the boundaries.
In recent years, there have also appeared a binary mask for ArF excimer laser light using a material containing a molybdenum silicide compound as a light-shielding film, and the like.